Use --stdin-filename conditionally for mix-format (#322)

Closes #319 because this does the same thing but it transparently works
for all versions of mix-format.

CHANGELOG.md

@@ -27,6 +27,9 @@ The format is based on [Keep a Changelog].
   the project ([#301]).
 * Ormolu is now passed the `--stdin-input-file` argument, which has
   become required ([#312]).
+* `mix format` is now passed the `--stdin-filename` argument which is
+  required in some cases. The version of Mix is autodetected and this
+  option is only passed when it is supported ([#319]).
 
 ## Internal
 * Improvements to formatter test framework, it is now possible to
@@ -38,6 +41,7 @@ The format is based on [Keep a Changelog].
 [#313]: https://github.com/radian-software/apheleia/pull/313
 [#316]: https://github.com/radian-software/apheleia/pull/316
 [#317]: https://github.com/radian-software/apheleia/issues/317
+[#319]: https://github.com/radian-software/apheleia/pull/319
 
 ## 4.2 (released 2024-08-03)
 ### Changes

apheleia-formatters.el

@@ -91,7 +91,7 @@
     (ktlint . ("ktlint" "--log-level=none" "--stdin" "-F" "-"))
     (latexindent . ("latexindent" "--logfile=/dev/null"))
     (mix-format . ("apheleia-from-project-root"
-                   ".formatter.exs" "mix" "format" "-"))
+                   ".formatter.exs" "apheleia-mix-format" filepath))
     (nixfmt . ("nixfmt"))
     (ocamlformat . ("ocamlformat" "-" "--name" filepath
                     "--enable-outside-detected-project"))
@@ -1063,17 +1063,22 @@ purposes."
   ;; resolve for the whole formatting process (for example
   ;; `apheleia--current-process').
   (with-current-buffer buffer
-    (when-let ((exec-path
-                (append `(,(expand-file-name
-                            "scripts/formatters"
-                            (file-name-directory
-                             (file-truename
-                              ;; Borrowed with love from Magit
-                              (let ((load-suffixes '(".el")))
-                                (locate-library "apheleia"))))))
-                        exec-path))
-               (ctx
-                (apheleia--formatter-context formatter command remote stdin)))
+    (when-let* ((script-dir (expand-file-name
+                             "scripts/formatters"
+                             (file-name-directory
+                              (file-truename
+                               ;; Borrowed with love from Magit
+                               (let ((load-suffixes '(".el")))
+                                 (locate-library "apheleia"))))))
+                ;; Gotta set both `exec-path' and the PATH env-var,
+                ;; the former is for Emacs itself while the latter is
+                ;; for subprocesses of the proc we start.
+                (exec-path (cons script-dir exec-path))
+                (process-environment
+                 (cons (concat "PATH=" script-dir ":" (getenv "PATH"))
+                       process-environment))
+                (ctx
+                 (apheleia--formatter-context formatter command remote stdin)))
       (if (executable-find (apheleia-formatter--arg1 ctx)
                            (eq apheleia-remote-algorithm 'remote))
           (apheleia--execute-formatter-process

scripts/formatters/apheleia-mix-format

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if (( "$#" != 1 )); then
+    echo >&2 "usage: apheleia-mix-format PATH"
+    exit 1
+fi
+
+path="$1"
+
+mix_binary="$(which mix)"
+checksum="$(md5sum "${mix_binary}" | awk '{print $1}')"
+
+cache_dir="${XDG_CACHE_DIR:-${HOME}/.cache}/apheleia"
+ver_file="${cache_dir}/mix-format-version-${checksum}"
+
+if [[ ! -f "${ver_file}" ]]; then
+    mkdir -p "$(dirname "${ver_file}")"
+    mix --version </dev/null | \
+        grep -Eo 'Mix [^ ]+' | \
+        awk '{print $2}' > "${ver_file}"
+fi
+
+ver="$(< "${ver_file}")"
+needed_ver="1.14.0"
+higher_ver="$( (echo "${ver}"; echo "${needed_ver}") | sort -V | tail -n1)"
+
+args=(mix format)
+if [[ "${ver}" == "${higher_ver}" ]]; then
+    args+=(--stdin-filename "${path}")
+fi
+args+=(-)
+
+exec "${args[@]}"

test/formatters/apheleia-ft.el

@@ -323,6 +323,12 @@ returned context."
   (interactive
    (unless (or current-prefix-arg noninteractive)
      (list (completing-read "Formatter: " (apheleia-ft--get-formatters)))))
+  ;; Yeah this code is super duplicative and really we should just
+  ;; refactor the original `apheleia--run-formatter-process' to be
+  ;; testable and run that instead. It would better ensure that
+  ;; behavior is the same between the test suite and the actual
+  ;; runtime. That is a future project. Or it could be a now project
+  ;; if you, dear reader, are feeling up to it.
   (dolist (formatter (or formatters (apheleia-ft--get-formatters)))
     (dolist (in-file (apheleia-ft--input-files formatter))
       (let* ((extension (file-name-extension in-file))
@@ -337,15 +343,17 @@ returned context."
              (exit-status nil)
              (out-file (replace-regexp-in-string
                         "/in\\([^/]+\\)" "/out\\1" in-file 'fixedcase))
-             (exec-path
-              (append `(,(expand-file-name
+             (script-dir (expand-file-name
                           "scripts/formatters"
                           (file-name-directory
                            (file-truename
                             ;; Borrowed with love from Magit
                             (let ((load-suffixes '(".el")))
                               (locate-library "apheleia"))))))
-                      exec-path))
+             (exec-path (cons script-dir exec-path))
+             (process-environment
+              (cons (concat "PATH=" script-dir ":" (getenv "PATH"))
+                    process-environment))
              (display-fname
               (replace-regexp-in-string
                (concat "^" (regexp-quote